The mass is big, the gravity is big, and the upward reaction force (i.e. resistance) is also big, so it landed at the same time. Galileo (1564-1642), an Italian physicist, astronomer and philosopher, was the pioneer of modern experimental science. 1590, Galileo leaned in Pisa. From then on, Aristotle's theory that "the falling speed of an object is proportional to its weight" was overthrown, and the wrong conclusion that lasted for 1900 years was corrected. Before Galileo, Aristotle in ancient Greece believed that the falling speed of an object was different. Its falling speed was proportional to its weight, and the heavier the object, the faster it fell. For example, an object weighing 10 kg. The falling speed is faster than that of 1 kg. 10 times. 1700 years ago, people have always regarded this theory that violates the laws of nature as an unquestionable truth. Young Galileo boldly questioned Aristotle's theory according to his own empirical reasoning. After careful consideration, he decided to do an experiment by himself. He chose the leaning tower of Pisa for the experiment. The other one, weighing 1 lb, is hollow. Galileo stood on the leaning tower of Pisa and looked under it. The tower was full of people who came to watch, and everyone talked about it. Someone sarcastically said, "This young man must be out of his mind! Aristotle's theory cannot be wrong! " The experiment began. Galileo took an iron ball in each hand and shouted, "Look clearly, people below, the iron ball is about to fall." Then he opened his hands at the same time. People saw that the two iron balls fell parallel and fell to the ground almost at the same time. Everyone was dumbfounded. Galileo's experiment revealed the secret of falling body movement and overthrew Aristotle's theory. This experiment was in physics.